Friday, February 9, 2018

Deep Dive: How Unusual Is Our Snowfall and Snowpack This Season?

Skate skiing on the "Greatest Snow on Earth" at the Utah Olympic Park late yesterday
left much to be desired.
Following up on the previous post, let's take a deep dive and see how unusual this year has been so far for snowfall and snowpack.

This is perhaps an even more challenging topic than temperature.  Measurements of snowfall and snowpack are spotty and continuous records going back to before 1990, when most SNOTEL stations were installed, are difficult to find.  In addition, snowpack is strongly influenced by changes in vegetation and human activity around observing sites, not to mention factors such as wind transport.  

For snowfall, our best option is the meticulous record kept by snow rangers and avalanche professionals at Alta Guard, which is being extended and maintained today by the UDOT Avalanche Safety Office in Little Cottonwood Canyon (big hat tip to them!).  Observations were collected at the Atwater study plot above the Town of Alta Municipal Offices through 1998, after which they have been collected at a site just west of Our Lady of the Snows.  These sites are about 400 or 500 meters apart.  

Snowfall at Alta Guard for the months of November through January (blue bars below) averages 249 inches, with significant variations from year to year.  Although a linear fit to this data shows no significant trend (blue dotted line) one can see some important variations on shorter time scales.  The late 50s and early 60s featured several poor snow years, whereas the 1980s and 1990s were generally fat, with Nov-Jan snowfall consistently above average.  Since 2000, we've seen an high frequency of seasons with below average Nov-Jan snowfall.  Similar trends are seen for liquid precipitation equivalent of snowfall (orange lines). 

The bars highlighted in red highlight Nov-Jan snowfalls that are below 170 inches, which is one standard deviation below the mean.  These represent especially poor starts to the snow season.  The worst on record is 1976/77, when only 81" was observed.  This season, 2017/18, 109" fell.  Not far behind are 1960/61 (116") and 1959/60 (121").  These are very close analogs for snowfall amount.  Five other seasons since 2000 fall into the poor start category, with 2002/03 being the next worse to this season with 128".

SNOTEL observations of snowpack are easy to access and provide daily data, but they start in the 1980s.  An unfortunate reality of my business is that the atmosphere exhibits a great deal of variability and 30-40 years provides a very short sample.  It's like rolling two dice a few times and hoping you get a good probability sample.

Another option is snow course observations, which are collected manually near the end of the month, using coring tubes, by the Natural Resources Conservation Service.

Observations at the end of January or early February were collected at a snow course site north of Parley's summit at an elevation of 7500 ft from 1952-2002.  Starting in 1979, a SNOTEL site was operated at a nearby, slightly higher location (7584 ft).  Data from these two sites is presented below.  One sees considerable variability, but curiously, there are ten seasons with lower snowpack water equivalent than the 6.8" observed this season on 1 February.  February 1977 is the big loser with only 2.8".  Also apparent is a paucity of "fat" late January/early February snowpacks since the late 1990s, consistent with the Alta snowfall record above.

Another option is the Mill D South snow course in Big Cottonwood Canyon (7400 ft).  Observations in late January and early February have been collected here since 1956, although a house built near the site in the early 2000s may influence measurements.

Here we also see considerable year-to-year variability in snowpack water equivalent.  Curiously, last season featured the highest value in the record, followed by this season's pathetic situation.  This season's late Jan/early February value of 5.3" is eclipsed only by 1977 (2.3") and 1981 (4.9").  Years only slightly better include 1961 (5.4"), 19060 (5.5"), 1963 (5.6"), 1992 (6.6"), 2003 (6.3"), 2007 (6.6"), and 2014 (6.8").

Finally, we have Brighton, where we can amalgamate observations from three sites, Silver Lake (with observations back to the 1930s!), Brighton Cabin (1961-present), and the Brighton SNOTEL (since 1986).  Again, significant variability from year to year.  Late January/Early February 1977 is still the big loser, with only 2.6" or 4.2" of water depending on measuring site.  Aforementioned years in the early 60s also look poor.  The Brighton SNOTEL (grey line) is prone to having lower values than the other sites, and this is quite apparent in low snow years.

Obviously, the picture one gets from this analysis is clear for some conclusions and muddy for others.  This reflects a number of factors, including the difficulty of snowfall and snowpack measurements, changes in site characteristics or sampling procedures, and the fact that snowfall and snowpack evolution feature tremendous spatial variability.

However, it is clear that if you are looking to crown the champion of crappy early (Nov-Jan) ski seasons, 1976/77 is the clear winner.  It is also clear that the 1980s and 1990s were very healthy for early season snow, and that the late 1950s and early 1960s, as well the first part of the 21st century, featured a high frequency of relatively poor early season snow and snowpack years.

Sorry kiddos, but your parents, shredding in the 80s and 90s, had it better than you.

Now for some words of caution.  Observations are often treated as "truth", but all observations have their errors and uncertainties.  I haven't dug deeply into these issues in this blog post.  Second, there is a difference between a trend and trend attribution.  Explaining why we have periods of poor or good early season snowfall is challenging.  Teasing out the influence of long-term global warming from climate variations in recent years is also challenging, as is possible contributions of dust-on-snow and other climate factors.  I am not tackling those issues here.  Finally, this analysis focuses on stations above 7000 ft.

In a future post, we may do an even deeper dive by examining what is happening at the end of the snow accumulation season.


  1. Yikes, can you imagine if Salt Lake were hosting the winter Olympics this winter, especially for Soldier Hallow? Were there contingency plans in place if 2002 had been like this year?

    1. Soldier Hollow is currently open for skiing, but they have 3-km open. They had some problems with their snowmaking system this year, which is why the terrain is o limited. That will need to be upgraded for a future Olympics. Natural snow is not needed for the Games (see PyeongChang and Beijing). If the Olympics were held this year, it would be ugly, but the show would go on.


  2. Excellent analysis! That was entertaining.

  3. Against all odds; Skiing at the Ho was killer yesterday for the annual WCS 10k! The Ho always delivers even if it is a limited amount of k's.

  4. So is it likely that this trend will continue? We've definitely had more dismal seasons than in the 80's and 90's, should we expect this to get worse? Are our days of consistently good winters over?

    1. I don't know the answer to that question. The long-term trend over the next several decades is one with a warmer future that will certainly impact lower-to-mid elevation snowpack and snowfall. What we get over the next decade or two, however, is dependent as well on the whims of the jet stream, which we lack the ability to predict over such periods.